Process for the preparation of mordenite

ABSTRACT

High purity mordentie having a very small particle size is prepared at temperatures below 160* C by heating an aqueous mixture of amorphous silica-alumina having a silica/alumina molar ratio between 9.5 and 12.5 and one or more sodium compounds wherein at least 70 mol percent of the sodium, as Na2O, originates from sodium salts of polybasic acids having a pK value &gt; 10 at 18* C for the highest dissociation step. The relation between the Na2O/Al2O3 molar ratio, m, in the starting mixture and the applied reaction temperature, t, which is 160* C or lower, is m 8.3-0.06 (t- 100) + OR - 2.3.

United States Patent [1 1 Kouwenhoven et al.

[ 51 Sept. 11, 1973 Cole, both of 3, Badhuisweg, Amsterdam, Netherlands22 Filed: Mar. 18,1971

21 1 Appl. No.: 125,845

[30] Foreign Application Priority Data Apr. 3, 1970 Netherlands 7015942[56] References Cited UNITED STATES PATENTS Kouwenhoven et al. 23/1133,328,119 6/1967 Robson 23/113 FOREIGN PATENTS OR APPLICATIONS 984,5022/1965 Great Britain 23/1 13 OTHER PUBLlCATIONS Barrer et al. J. Chem.Soc. 1965, pages 6621-6628 Primary ExaminerEdward J. Meros Attorney.lohnM. Duncan and Glen R. Grunewald [5 7 ABSTRACT High purity mordentiehaving a very small particle size is prepared at temperatures below 160Cby heating an aqueous mixture of amorphous silica-alumina having asilica/alumina molar ratio between 9.5 and 12.5 and one or more sodiumcompounds wherein at least 70 mol percent of the sodium, as Na,0,originates from sodium salts of polybasic acids having a pK value 10 at18C for the highest dissociation step. The relation between the Na,O/AlO molar ratio, m, in the starting mixture and the applied reactiontemperature, 2, which is 160C or lower, is m 8.3-0.06 (t100) 2.3.

8 Claims, No Drawings PROCESS FOR THE PREPARATION OF MORDENITEBACKGROUND OF THE INVENTION The invention relates to a process for thepreparation of mordenite at a relatively low temperature, starting fromamorphous silica-alumina.

Mordenite is a zeolite of the aluminosilicate type with the followingcomposition expressed in moles of the oxides: l.0 i 0.2 Na O'Al O i 0.5SiO It may occur either in hydrated or in dehydrated form. Mordenitevhas recently become highly popular because of its suitability as acarrier material for isomerization and hydrocracking catalysts.

Zeolites of the aluminosilicate type are usually prepared by keeping anaqueous alkaline mixture comprising certain amounts of one or morealuminum compounds and one or more silicon compounds at an ele vatedtemperature for some time and subsequently separating the zeolite formedfrom the mother liquor.

A preferred method for preparing mordenite involves heating an aqueousalkaline mixture with the following composition expressed inmoles of theoxides: 1.2 2.8 Na O'A1 O 9.5-l2.5 SiO,. 60-300 H O comprising amorphoussilica-alumina, sodium hydroxide and water, under pressure for 4-40hours at a temperature of l80260C and subsequently the mordenite formedis separated from the mother liquor. This preparation method, startingfrom amorphous silica-alumina, offers the advantage over preparationprocedures in which other aluminum and silicon sources are applied, thata synthetic mordenite is obtained which has very low contamination withzeolites different from mordenite and/or amorphous material. A drawbackof this method of preparing mordenite is, however, that a relativelyhigh reaction temperature of at least 180C is re quired. These hightemperatures generate high pressures and require expensive processequipment.- Below this temperature products are formed comprising lessthan 80%w of mordenite and/or more than 5%w of zeolites different frommordenite. Efforts to improve the process in this respect gave ratherdisappointing results. Although it is possible to carry out thepreparation at a lower temperature by increasing the reaction time withor without an increase of the amount of sodium hydroxide, these measuresonly lead to minor improvements. To prepare mordenite with the same highquality as before, a small decrease in reaction temperature requires avery large increase in reaction time. A further decrease in reactiontemperature results in reaction times longer than 350 hours beingrequired, which are no longer attractive from an economic point of view.Although increasing the concentration of sodium hydroxide in thestarting mixture has a beneficial influence on the temperature-timerelationship of the reaction, this measure can only be applied to acertain extent since it has appeared that if the concentration of sodiumhydroxide in the starting mixture expressed as molar ratio Na O/AMO, israised above 3.5, the mordenite prepared is contaminated with analcite.As the concentration of sodium hydroxide is further increased, moreanalcite is formed. In general it may be said that it is not possible toprepare, within 350 hours and at a temperature of 160C or lower, aproduct comprising at least 80%w of mordenite and at most 5%w ofzeolites different from mordenite, from an aqueous alkaline mixturecomprising amorphous silica-alumina, if sodium hydroxide is used assource for sodium.

SUMMARY OF THE INVENTION Very pure mordenite having a particle sizeabout one tenth the normal size can be prepared from an aqueous mixturecomprising amorphous silica-alumina having a silica/alumina molar ratiobetween 9.5 and 12.5 and one or more sodium compounds at a temperatureof 160C or lower and in a reasonable time, if at least mol.% of thesodium present in the starting mixture expressed as Na,O originates fromsodium salts of a certain class of polybasic acids. The polybasic acidsconcerned are those having a pK value 10 at 18C for the highestdissociation step, e.g., H PO and H CO The required sodium concentrationin the starting mixture depends on the reaction temperature applied asfollows. At a reaction temperature I as measured in degrees centigrade,the required sodium concentration in the starting mixture (m) expressedas molar ratio Na,O/Al,0, is given by the formula m 8.33-0.06 (t i 2.3,where t is 160C or lower.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to aprocess for the preparation'of mordenite by heating an aqueous mixturecomprising amorphous silica-alumina and one or more sodium compounds,wherein at least 70 mol.% of the sodium present in the starting mixtureexpressed as Na,O, originates from sodium salts of polybasic acidshaving a pK value for the highest dissociation step measured at 18C,which is larger than lOand wherein the following relation exists betweenthe l-Ia,()/Al,0 molar ratio (m) in the starting mixture and the appliedreaction temperature (t), which amounts at most to 160C: m 8.3-0.06(P100): 2.3.

If the preparation of mordenite according to the invention is, e.g.,carried out at a temperature of C, the sodium concentration in thestarting mixture expressed as-molar ratio Na,O/Al,0, should be at least3.0 and at most 7.6. If the preparation of mordenite according to theinvention is, e.g., carried out at a temperature of 100C the sodiumconcentration in the starting mixture expressed as molar ratio Nap/A1 0,should be at least 6.0 and at most 10.6. If at the temperaturesconcerned sodium concentrations outside these ranges are applied,products are formed comprising less than 80%w of mordenite and/or morethan 5%w of zeolites different from mordenite. It is very surprisingthat in contrast with sodium hydroxide, the present sodium salts aresuitable for the preparation of mordenite at temperatures of C andlower, since sodium hydroxide and the present sodium salts show acomparable performance if applied for the preparation of mordenite fromamorphous silica-alumina at higher temperatures.

Sodium salts suitable for the preparation of mordenite according to theinvention include sodium salts of both inorganic acids and organic acidsprovided that these acids fulfill the condition that the pK value oftheir highest dissociation step measured at 18C is larger than 10.Examples of suitable inorganic acids are P0,. Of the sodium salts used,only the sodium is incorporated in the mordenite.

In the starting mixture according to the invention, comprising amorphoussilica-alumina, water and one or more of the above-defined sodium salts,minor amounts of other sodium compounds may be present. provided thattheir concentration expressed as moles Na o is less than 30 percent ofthe total sodium concentration in the starting mixture, also expressedas mole Na O. As an example of such a sodium compound sodium hydroxidemay be mentioned. The preparation or mordenite according to theinvention, is however, preferably carried out, starting from a mixturein which the sodium originates completely or substantially completelyfrom one or more of the above-defined sodium salts. The amount of sodiumto be applied depends on the amount of alumina present in the startingmixture and on the temperature at which the reaction is carried out. Theamount of water present in the starting mixture may vary between widelimits. Usually the starting mixture contains 60-300 moles of water foreach mole of alumina present therein. The amorphous silica-aluminapreferably has a silica/alumina molar ratio between 9.5 and 12.5. Asamorphous silica-alumina preferably a cogel of aluminum hydroxide onsilica hydrogel is applied. The term cogel is used here to refer to anamorphous silica-alumina obtained by precipitating on silica hydrogel analuminum hydroxide gel. A cogel thus defined is therefore not acoprecipitate, since in the preparation of a coprecipitate silicahydrogel and aluminum hydroxide gel are simultaneously or almostsimultaneously precipitated from the solution. It is as sumed that inthe cogel silica globules are covered with a layer of alumina. A verysuitable method of preparing a silica-alumina cogel comprises firstprecipitating a silica hydrogel from an aqueous solution containingsilicate ions by addition of a mineral acid, subsequently adding analuminum salt to the mixture, and finally precipitating an aluminumhydroxide gel by addition of an alkaline-reacting solution. Instead of acogel obtained by the above-described process, the cogel may verysuitably be a commercial silica-alumina cracking catalyst with a lowalumina content. Such cracking catalysts usually have an alumina contentof about lll5%w, and are also obtained as a cogel.

The preparation of mordenite according to the invention is carried outby keeping the starting mixture at an elevated temperature for sometime. The preparation may be carried out at atmospheric pressure as wellas elevated pressure. If use is made of reaction temperatures higherthan the boiling point of the mixture, it is preferred to carry out theprocess in an autoclave at autogeneous pressure. The preparation ofmordenite according to the invention is preferably carried out at areaction temperature betewen 95 and 155C. At these temperatures muchlower pressures are gener ated than at the higher temperatures of priorprocesses.

From an economic point of view it is desirable to keep the reaction timeas short as possible. Since the reaction time depends among otherfactors on the reaction temperature and on the amount of sodium presentin the starting mixture, these two variables are preferably chosen insuch a way in relation to each other that the formation of a very puremordenite takes place as quickly as possible.

During the preparation, the reaction mixture is preferably agitated,since this has a beneficial influence on the yield of mordenite. Thismay be effected for instance by stirring, or shaking. After theformation of the mordenite, the crystals are separated from the motherliquor, for instance by filtration, decanting or centrifuging. The massof crystals isthen washed with water and finally dried at a temperaturebetween and 200C.

Mordenite prepared according to the invention, using a silica-aluminacogel as amorphous silicaalumina, is obtained as a very fine powder witha crystal size of from 0.1 to 10;]. Thisis about one tenth the size ofmordenite particles prepared from processes which employ highertemperatures and NaOH. For some applications of mordenite is is oftendesirable to have the mordenite available in larger particles. For thispurpose the mordenite may be mixed with an inert binder and shaped intoparticles with a certain form or size. This technique is well known,e.g., in the preparation of catalyst carriers, and need not be describedin greater detail. Examples of suitable binders are natural clays suchas kaolin and bentonite and synthetic inorganic oxides such as alumina,silica, boria and zirconia or combinations thereof, such assilica-alumina and silica-zirconia.

Mordenite prepared according to the invention may be used for variousapplications, such as an adsorbent, as a molecular sieve for theseparation of hydrocarbon mixtures as well as for the separation ofgases, as a catalyst carrier and the like. In view of itshigh degree ofpurity mordenite prepared according to the invention is especiallysuitable as a catalyst carrier. Catalysts with excellent performance inhydrocarbon conversion processes, especially isomerization andhydrocracking catalysts, can be obtained by loading the mordenite, withor without using a binder, as. described, with one or;

more metals of Group VIB, VIIB and/or VIII of the Periodic System ofElements.

The invention will now be further elucidated with the aid of thefollowing examples.

In case reaction temperatures were applied above the boiling point ofthe mixture, the reaction was carried out in a closed vessel atautogeneous pressure. The composition of the products was establishedwith the aid of X-ray analysis. In all experiments use was made of acommercial amorphous silica-alumina cracking catalyst having a watercontent of 25%w and comprising 14%w of alumina and 86%w of silicacalculated on dry material, as amorphous silica-alumina.

EXAMPLE I TABLE I Amount of NaOH present in starting mixture, expressedas molar ratio Na,0/Al,0,

reaction time hours reaction temp.

Exp. No.

composition of the product obtained,v %w

1 L8 220 12 95 mordenite 5 amorphous material 2 2.2 200 48 95 mordenite5 amorphous material 3 1.8 160 72 100 amorphous material 4 4 150 72 100analcite 5 4 210 16 l analcite EXAMPLE II Eleven mixtures of the molarcomposition: x Na PO -Al O -10.4 SiO 253 H O were prepared by slowlyadding with stirring a certain amount of Na PO 'l 2 H O to a mixture of46 g of the above-described cracking catalyst in water. The mixtureswere heated with stirring at a certain temperature and for a certaintime. After the reaction mixture had cooled, the solid material wasfiltered ofi, washed with water until the pH of the filtrate was lowerthan 10 and dried at 120C. The conditions and results of theseexperiments are summarized in Table II.

TABLE II Amount Exp. of Na,PO reaction reaction composition of presentin starttemp. time the product obing mixture, ex- "C hours tained, kwpressed as molar ratio Na,O/Al,0,

2.0 150 72 100 amorphous material 7 3.5 150 72 95 mordenite amorphousmaterial 8 4.5 150 72 95 mordenite 5 amorphous material 9 6.0 U0 72 90mordenite 10 amorphous material l0 8.0 150 72 50 mordenite 50 analcite ll 2.0 100 300 100 amorphous material l2 6.0 100 320 90 mordenite 10amorphous material 13 8.0 100 320 95 mordenite 5 amorphous material 149.0 100 172 90 mordenite 10 amorphous material 15 10.5 I00 240 90mordenite 3 gmelenite 7 amorphous material I6 12.0 l00 H2 50 gmelenite50 amorphous material Of experiments ll6, only 7-9 and 12-15 areaccording to the present invention. The other experiments are given forcomparative purposes. A chemical analysis of the products resulting fromexperiments 7-9 and l2-l5 showed that no phosphorus was present therein.

We claim as our invention:

1. A process for the preparation of mordenite which comprises heating anaqueous mixture of amorphous silica-alumina having a silica/aluminamolar ratio between 9.5 and 12.5 and one or more sodium compoundswherein at least mol.% of the sodium present in the starting material,expressed as Na O, originates from sodium salts of polybasic acidshaving a pK value greater than 10 at 18C for the highest dissociationstep, and wherein the molar ratio, m, of Na O/Al O in the startingmixture and the applied reaction temperature, I, which expressed indegrees centigrade is at most 160C, is m 8.3 0.06 (t-lOO) 1*: 2.3.

2. The process of claim 1 wherein the sodium salts of polybasic acidsare sodium salts of orthophosphoric acid or carbonic acid.

3. The process of claim 2 wherein the sodium salt is Na PO 4. Theprocess of claim 1 wherein the amorphous silica-alumina is a cogel ofaluminum hydroxide on silica hydrogel.

5. The process of claim 4 wherein the silica-alumina cogel has beenprepared by a procedure which comprises first precipitating a silicahydrogel from an aqueous solution containing silicate ions by adding amineral acid, subsequently adding an aluminum salt to the mixture, andfinally precipitating an aluminum hydroxide gel by adding analkaline-reacting solution.

6. The process of claim 4 wherein the silica-alumina cogel is acommercial cracking catalyst with a low alumina content 7. The processof claim 1 wherein the reaction temperature is between and C.

' 8. The process of claim 1 wherin the reaction mixture is agitatedduring the preparation.

2. The process of claim 1 wherein the sodium salts of polybasic acidsare sodium salts of orthophosphoric acid or carbonic acid.
 3. Theprocess of claim 2 wherein the sodium salt is Na3PO4.
 4. The process ofclaim 1 wherein the amorphous silica-alumina is a cogel of aluminumhydroxide on silica hydrogel.
 5. The process of claim 4 wherein thesilica-alumina cogel has been prepAred by a procedure which comprisesfirst precipitating a silica hydrogel from an aqueous solutioncontaining silicate ions by adding a mineral acid, subsequently addingan aluminum salt to the mixture, and finally precipitating an aluminumhydroxide gel by adding an alkaline-reacting solution.
 6. The process ofclaim 4 wherein the silica-alumina cogel is a commercial crackingcatalyst with a low alumina content
 7. The process of claim 1 whereinthe reaction temperature is between 95* and 155*C.
 8. The process ofclaim 1 wherin the reaction mixture is agitated during the preparation.